1. Field of the Invention
The present invention generally relates to control of deposition processes in the manufacture of semiconductor devices and, more particularly, to the elimination of starvation of the deposition process upon initiation of Low Pressure Chemical Vapor Deposition (LPCVD) after an idle period due to exposure to a deleterious vapor or a lack of correct feed vapor composition, using infrared source verification.
2. Description of the Prior Art
Compositions of reactive vapors have been analyzed within a Chemical Vapor Deposition (CVD) reactor using a vapor by-pass and flame emission spectroscopy.
Gas analyzers, such as hydrogen flame ionization detector or thermal conductivity detector, have been used to measure and control the flow of raw materials into reactors used for deposition on superconducting films. With this method, the concentration of gases in the primary gas stream is not sampled directly. Also, the measurement technique does not allow measurements to be made in real-time while the gas is flowing to the reactor.
Gas analyzers have also been used to measure the concentration of a reactant gas and to control the rate of gas supply from an auxiliary gas supply. With such a method, the reactant gas is not sampled directly in the delivery lines leading to the chamber, but sampled indirectly through a tube inserted into the reactor. Because of the method of gas sampling, the workpiece is exposed to potentially undesirable chemicals.
Fourier Transform Infrared (FTIR) spectroscopy has been used to perform online gas analysis of a multicomponent gas flow from a combustion engine. This method measures the components present in an exhaust stream, but not the reactants in an input stream. The FTIR sensor performs measurements after the reaction process not before and measures only a diluted gas sample.
The prior art does not sample gas directly through a line which leads to a gas collector and separation column, monitoring the gas stream nondestructively prior to exposing the workpiece. The prior art does not describe a control scheme where the measurements of the gas concentrations are used to switch the input stream. A closed circuit valve controller activated by an FTIR output to redirect the reactive gas from the CVD reactor to a bypass connector used jointly with an in-line FTIR cell for the analysis of the reactive gas being supplied to a generalized CVD reactor, has not been taught previously. In a CVD system, it is important that the reactor is not exposed to potentially deleterious impurities, so monitoring must be performed prior to allowing gases to enter the reactor.